The present invention relates to load lifting and lowering hoists of the type having multiple columns and, more particularly, to safety mechanisms therefor.
Typically, vehicle hoists of the multi-post type include lifting mechanisms, e.g., screw jacks, in each post that are synchronously driven by an endless member, e.g., a sprocket chain. The power source for the endless member may be incorporated into the load bearing carriage of the lifting mechanism of one of the columns, referred to as a drive column. The load bearing elements of all of the columns are thus raised or lowered in unison while engaging opposite sides or ends of the vehicle carried thereon.
A serious problem inherent with such hoists is that breakage of the endless chain stops the vertical movement of only the idler column or columns, the drive column continuing to operate. As a consequence, if the hoist is in the process of raising or lowering a vehicle, the drive column continues to lift or lower the vehicle portion engaged thereby to tilt it to an unstable and unsafe position, in which there is a danger that the vehicle may tumble or fall from the hoist. As is apparent, such malfunction can cause serious damage to the vehicle as well as other property damage and grave personal injury.
At present, some of the currently available multipost hoists do not incorporate any safeguards for stopping the operation of the hoist whenever the endless member breaks. Other currently available hoists of this type do incorporate such safeguards which, however, have generally been unduly complicated and expensive, thus inhibiting widespread usage thereof.